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The Mechanical properties and fracture behavior of nanocomposites and carbon fiber composites (CFRPs) containing organoclay in the epoxy matrix have been investigated. Morphological studies using TEM and XRD revealed that the clay particles within the epoxy resin were intercalated or orderly exfoliated. The organoclay brought about a significant improvement in flexural modulus, especially in the first few wt% of loading, and the improvement of flexural modulus was at the expense of a reduction in flexural strength. The quasi-static fracture toughness increased, whereas the impact fracture toughness dropped sharply with increasing the clay content.Flexural properties of CFRPs containing organoclay modified epoxy matrix generally followed the trend similar to the epoxy nanocomposite although the variation was much smaller for the CFRPs. Both the initiation and propagation values of model I interlaminar fracture toughness of CFRP composites increased with increasing clay concentration. In particular, the propagation fracture toughness almost doubled with 7wt% clay loading. A strong correlation was established between the fracture toughness of organoclay-modified epoxy matrix and the CFRP composite interlaminar fracture toughness.

The environmental degradation mechanisms of epoxy-organoclay nanocomposites due to accelerated UV and moisture exposure are studied. Various characterisation tools, including FTIR, SEM, XRD and XRF analyses, were used to evaluate the effects of clay content on the progressive changes in chemical element, topography and colour of the nanocomposite. It is found that microcracks started to appear on both the neat epoxy and nanocomposite surface after about 300 h of UV exposure. The nanocomposite exhibited thicker and shallower cracks with a less degree of discoloration than the neat epoxy due to the diffusion barrier characteristics of organoclay with high aspect ratio. The presence of transition metal ions along with low-molecular-weight organic modifiers in organoclay, however, accelerated the degradation of polymer, counterbalancing the above ameliorating barrier properties of clay. FTIR analysis indicated that photo-degradation generated carbonyl groups by chain scission and the rate was slightly higher for the nanocomposites than for the neat epoxy. While moisture further accelerated the photo-degradation process through the enhanced mobility of free radicals and ions, the organoclay could limit the deteriorating effect of moisture, resulting in much better overall resistance to photo-degradation in the presence of moisture for the nanocomposite than the neat epoxy.

The residual mechanical properties of epoxy-organoclay nanocomposites after moisture and UV exposure have been evaluated. The flexural modulus decreased after moisture saturation, with much less extent for the nanocomposite than the neat epoxy. The tensile failure strain was significantly reduced with UV exposure time due to the embrittlement effect, and the addition of organoclay mitigated the failure strain reduction. The elastic modulus varied little with UV exposure time regardless of organoclay, because the modulus was determined by the core material which was unaffected by UV exposure. The microhardness and the modulus of the surface material determined from nanoindentation tests increased after UV exposure, with less extent in the nanocomposite than the neat epoxy due to the thinner embrittled top layer for the nanocomposite. All these observations confirmed the beneficial effects of organoclay in improving the barrier characteristics against UV exposure.

The barrier performance of silane/clay nanocomposites as a coating material on concrete structure has been evaluated under different accelerated weathering tests, including moisture permeability and salty water spray. The silane/clay nanocomposite was fabricated by curing the silane-organoclay mixture through hydrogen bonding with concrete. XRD analysis indicated an improved intercalation of clay after adding into the silane solution. SEM examination of the coated concrete surface confirmed that the nanocomposite can effectively cover the pores and voids present on the concrete surface. The rheological study revealed a linear increase in viscosity with the addition of clay. Wetting properties were evaluated via contact angle measurements. The moisture permeability test showed that the permeability was substantially reduced due to the presence of clay of high aspect ratio. The salty water spray tests indicated the distinct barrier characteristics of silane/clay nanocomposite coating on concrete structure.

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